Metallurgical oven and a material basket for a metallurgical oven

ABSTRACT

The invention relates to a metallurgical furnace with a vessel ( 10 ), a cover ( 20 ) for the vessel, a charging device ( 30 ) for charging material that will be melted in said vessel, which charging device has a rotatable retaining means ( 31 ) and a volume (C) for receiving charging material, and a projection ( 40 ) provided in the charging opening ( 42 ) and which is arranged on the cover ( 20 ) or on the vessel ( 10 ). The furnace has a maximum filling level (H 2 ), the rotatable retaining means is pivoted for charging into the projection, the vessel, the cover, the charging device, the retaining element and the projection are dimensioned in such a way that the pivoting range of the retaining means is higher than the maximum filling level (H 2 ). The invention is characterised in that the charging device comprises at least two self-supporting material baskets ( 32 ) that can be positioned in a removable manner above the projection ( 40 ), which comprise respectively an inner chamber that can be closed on the lower side of the material basket ( 32 ) by the retaining means ( 31 ) and also a volume (C) for receiving the charging materials and a change device ( 33 ) provided for interchanging and positioning the material basket ( 32 ).

CROSS-REFERENCE

[0001] This application is the national stage filing of InternationalApplication No. PCT/EP02/09255, which was filed Aug. 19, 2002 andclaimed priority to German Patent Application No. 101 40 805.6 filedAug. 20, 2001.

TECHNICAL FIELD

[0002] The invention concerns a metallurgical furnace, in particular anelectric arc furnace, and a material basket for the metallurgical art.

DESCRIPTION OF THE RELATED ART

[0003] A metallurgical furnace, such as the electric arc furnace knownfrom WO 98/08041 A1, has a vessel that comprises a lower vessel portionand an upper vessel portion, a cover for the vessel and a chargingapparatus, which is in the form of a shaft and in which a pivotableretaining means is arranged. In the smelting operation for suchapparatus, the entire charging material (for example, scrap) is chargedin one operation. Because the volume of the smelted material,particularly in the case of scrap, is substantially less than in thenon-molten condition, the volume defined by the vessel and the cover isnot sufficient to receive the entire amount of charging material for asmelting operation. Therefore, the portion of the charging material thatis not in the molten condition remains standing as a column within theshaft.

[0004] Consequently, the retaining means, which is formed by a pluralityof pivotably mounted fingers, cannot be pivoted back into the closedcondition until the column of the charging material has melted togetherto such an extent that the top side of the column is below the range ofpivotal movement of the retaining means (see in particular FIG. 4 of WO98/08041 A1).

[0005] In order to charge the entire amount of the charging materialinto the furnace all at once, the shaft must have a correspondingvolume, which means that the shaft must be very high due to the spatialrequirements, in particular the arrangement of the electrodes, in thearc furnace. In the alternative, the shaft may be designed only toreceive the amount of the charging material that will be charged in oneoperation. In that case, additional charging material must be chargedvia the shaft by means of a crane and a material basket (for example, ascrap basket). In any event, the shaft is loaded with the chargingmaterial from above, thereby meaning that sufficient space above theshaft must be provided for the loading apparatus, such as a crane or thelike. All in all, such an arrangement requires a very large height to beavailable above the shaft when the steel works are built.

[0006] When loading the shaft with the charging material, for examplewith scrap, the charging material drops from a height of 4 to 6 m,because the material must be dropped into the shaft from above. As aresult, there is a possibility of damaging the retaining member and/orthe shaft walls.

[0007] Because of the necessary structural height, an arc furnace of thekind described in WO 98/08041 A1 is normally constructed with a shaftthat is designed for half the necessary amount of charging material. Thebalance of the charging material for the smelting operation is chargedinto the furnace through the shaft from above by means of a materialbasket (scrap basket). Because only a portion of the charging material(scrap) that was stored in the shaft during the refining period for thepreceding charge is preheated, a considerable portion of the chargingmaterial is at a relatively low temperature at the beginning of thesmelting operation; thus the waste gas that passes through the shaft isat a very low temperature. For known reasons, that low temperature isdisadvantageous with respect to pollutants, in particular so-called VOCs(Volatile Organic Compounds). For example, VOCs must be incinerated at atemperature of about 700 to 800° C. and the resulting waste gas thenmust be quenched (rapidly cooled down) so that the renewed formation ofpollutants does not occur. The waste gas that passes through the shaftand the cold charging material is far from being at the appropriatetemperature, such that a considerable introduction of energy is requiredinto a post-combustion chamber in order to destroy the VOCs. Theadditional energy requirements results in increased operating costs.

[0008] Because the shaft and the retaining means formed by the fingersare supported on the furnace during all operating cycles, cooling of theretaining means and at least the lower part of the shaft is necessaryfor thermal reasons. The corresponding design configuration of the shaftmeans that a carrier structure is required for the shaft, which carrierstructure, on the one hand, holds the cooling system and the necessarysupply arrangements and, on the other hand, forms a sufficient supportdevice for the scrap that is charged via the shaft. In addition, duringthe charging operation of the charging material, in particular scrap,through the shaft, considerable dynamic forces occur due to the greatdropping height, and those forces entail the risk of damage to the shaftand the fingers, in particular the cooling arrangement. Due to the highdynamic forces involved, it is also necessary for the fingers of theretaining member to be individually mounted and to be replaceable in anexpensive and complicated configuration, for example with spring packs.That results in the structure having an increased complexity, and anincreased volume necessary due to the increased complexity, with respectto the retaining means.

[0009] Due to the foregoing aspects, the volume of the shaft, inparticular the presence of the carrier structure, the coolingarrangement, etc. is relatively large, such that, in order to maintainthe necessary spacing relative to the electrodes at the centre of thecover of the furnace vessel, the shaft must be disposed relatively faraway from the center in the direction of the edge of the cover or thevessel.

[0010] EP 0 672 881 A1 discloses an arc furnace having two chargingshafts, which shafts have charging openings that are arranged laterallyat the side walls of the unit formed by the vessel and the cover.

[0011] DE 44 24 324 A1 and DE 43 26 369 A1 each disclose retaining meansformed by divided fingers for a shaft. FIG. 1 of DE 44 24 324 A1illustrates an example of a conventional arc furnace in which a materialbasket 27 is disposed above the shaft for further charging of chargingmaterial, thereby requiring the above-described necessary internalheight above the shaft.

[0012] JP 7-332836 (A) discloses an arc furnace having a shaft in whichtwo charges are held one above the other, each by appropriate retainingmembers. The Steel Times International, November 1995, discloses theso-called ‘Daido MSP-DCArc Furnace’ that is also published in a paper ofthe SEAISI 1996 THAILAND CONFERENCE under the title “Development ofMSP-DC EAF Process.” That furnace has a charging apparatus in the formof a shaft. Two chambers are arranged in a perpendicularly mutuallysuperposed relationship in the shaft. Each of the chambers can be closedat its underside by a pivotable retaining means. The entire shaft can bedisplaced laterally with respect to the furnace vessel for maintenancepurposes or the like. The chambers of the shaft are loaded from above bymeans of a scrap basket.

SUMMARY OF THE INVENTION

[0013] The object of the present invention is to provide an improvedmetallurgical furnace and a material basket suitable for such a furnace.

[0014] This object is attained by the furnaces and material basketsdisclosed herein.

[0015] In a metallurgical furnace according to the present teachings,the retaining means can be pivoted back immediately after the chargingoperation in order to close the charging apparatus. This design resultsin a configuration of the charging apparatus with suitableinterchangeable material baskets, in which the corresponding materialbasket can be exchanged immediately after the unloading operation. Inaddition, this design provides an empty space in the upper region of theprojection, in which space it is possible to influence the waste gas.

[0016] When the charging apparatus is designed with the interchangeablematerial baskets, there is no need to provide cooling means for theretaining means and the shaft, because they do not heat up so greatly soas to require cooling, due to relatively short residence time above theprojection.

[0017] In addition, when the charging apparatus is designed with theinterchangeable material baskets, the need for a large internal heightabove the furnace is eliminated, because the material baskets can bereplaced by moving them laterally over the projection.

[0018] Because the empty space within the projection above the chargedmaterial is normally always above the firing temperature for combustingcoal dust and/or CO, the waste gas temperature/waste gas composition canbe adjusted in a very simple and inexpensive manner by simply injectingcoal dust and/or oxygen into the waste gas.

[0019] In such a configuration of the charging apparatus havinginterchangeable material baskets, there is no longer any need for ashaft carrier structure and a water cooling arrangement. Therefore, whenthe charging volume is the same, the corresponding material baskets canbe arranged substantially closer to the electrodes than known shafts.Therefore, it is possible to use a vessel shape that is round in planview, instead of a horseshoe shape.

[0020] Further features and advantages will be apparent from thedescription of embodiments by way of example with reference to theFigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 shows a metallurgical furnace of a first embodiment of theinvention in a front view a) in cross-section, a side view b) incross-section, which is taken from the left in FIG. 1a, and a plan viewc) in cross-section.

[0022]FIG. 2 shows the front view of FIG. 1a) in an enlarged scale.

[0023]FIG. 3 shows the side view of FIG. 1b) in an enlarged scale.

[0024]FIG. 4 shows the plan view of FIG. 1c) in an enlarged scale.

[0025]FIG. 5 shows the metallurgical furnace of the first embodiment ofFIG. 1 which, for operation as an arc furnace without a shaft, is closedby means of a cover, as a front view a) in cross-section, a side view b)in cross-section, which is taken from the left in FIG. 5a), and a planview c) in cross-section.

[0026]FIG. 6 shows the front view of FIG. 5a) in an enlarged scale.

[0027]FIG. 7 shows the side view of FIG. 5b) in an enlarged scale.

[0028]FIG. 8 shows the plan view of FIG. 5c) in an enlarged scale.

[0029]FIG. 9 shows a second embodiment of the metallurgical furnace as afront view a) in cross-section in a steel works, a side view b) incross-section, which is taken from the left in FIG. 9a), and a plan viewc) in cross-section.

[0030]FIG. 10 is a cross-sectional view of a material basket inaccordance with an embodiment of the invention, the material basketbeing disposed on a transport carriage.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Described hereinafter with reference to FIGS. 1 to 8 is a firstembodiment of a metallurgical furnace according to the invention, whichrepresents the preferred embodiment.

[0032] FIGS. 1 to 4 show the first embodiment in a first configurationin which material baskets 32, which can be positioned by means of achanging device 30 above a projection 40, are used as the shaft.

[0033] FIGS. 5 to 8 show a second configuration of the first embodiment,in which the charging opening 42 of the projection is closed by means ofa cover 43 in the melting operation in the manner of a conventional arcfurnace that does not have a shaft. That configuration can be used tocontinue operation when maintenance procedures are to be performed onthe changing device and/or the material baskets or the like.

[0034] The first configuration will now be described with reference toFIGS. 1 to 4.

[0035] The first embodiment is formed as an arc furnace 1 with a furnacevessel 10 supported on a furnace cradle 2. The furnace vessel 10comprises a lower vessel portion 11 formed by a brick-built furnacehearth and an upper vessel portion 12 that is formed in the usual mannerwith water-cooled elements. The furnace vessel has a bay 13 with a taphole 15 and a closure device 16 for the tap hole 15.

[0036] The furnace also has a cover 20 that is formed in the usualmanner with water-cooled elements and, which in the usual manner, hasopenings for the electrodes 71 to be introduced into and removed fromthe furnace vessel. In the first embodiment shown in FIGS. 1 to 4, thecover has a projection 40 that, in the plan view of the vessel 10 andthe cover 20, is disposed on one side of the electrodes. The projection40 is made of water-cooled elements and is joined to the cover 20.

[0037] In accordance with an alternative embodiment, the projection 40can also be formed separately from the cover 20. The projection 40 canthen be in the form of a separate part or part of the vessel 10.

[0038] Preferably, the projection 40 is part of the cover 20. In thatcase, the projection 40 can be lifted off together with the cover 20 bythe lifting device for the cover, for example during maintenanceoperations, and can be pivoted or moved away.

[0039] The projection 40 is substantially cylindrical with across-section that is substantially rectangular in the horizontaldirection. In the first embodiment shown in FIGS. 1 to 4, the projection40 has substantially perpendicular walls in the vertical direction ofthe furnace vessel. As can be seen from FIGS. 2 and 4, adaptation of thesubstantially rectangular shape of the projection to the substantiallyround cross-section (broken line 14 in FIG. 4), as viewed incross-section in the horizontal direction, of the furnace vessel, issubstantially effected by the side walls of the furnace vessel 12 havingan appropriate configuration.

[0040] In the alternative, the corresponding adaptation can be effectedby modifying the shape of the projection 40 so that the walls of thevessel 12 are perpendicular and adapted to the shape of the lower vesselportion. This alternative embodiment, which is not shown in FIGS. 1 to4, is preferred because it reduces the height from which the chargingmaterial drops on to the inclined walls, and the resulting dynamicloading thereon.

[0041] The projection 40 has an opening 41 laterally above the height H2and below the height H1, which opening 41 serves as an extractionopening for suctioning away waste gas. The extraction opening 41 isconnected via a waste gas conduit 61 to a waste gas main conduit 62 thatcommunicates with a post-combustion chamber 60. A controlled valve flap64 is provided in the waste gas conduit 61. The projection 40 has anupwardly open opening 42, which is a charging opening for the furnace.

[0042] A charging apparatus 30, which has a rotary tower or turret 33 asan embodiment of a changing device, is provided for the operation ofcharging the charging material. In the present case, scrap isexemplified as a batch material that is charged into the furnace usingthe charging apparatus 30.

[0043] In the first embodiment, an electrode arrangement 70 having anelectrode holding and displacement device 72 for holding and displacingthe electrodes 71 is arranged on one side (the left-hand side in FIG. 2)of the furnace vessel 10. The charging apparatus 30 is arranged on thecorresponding other side of the furnace vessel 10 (the right-hand sidein FIG. 2).

[0044] The changing device 33, which is in the form of a rotary tower,has two cantilever arms 34 that are displaced 180° about the verticalrotational axis 35 of the rotary tower 33, each being designed to hold arespective material basket 32. The cantilever arms 34 are dimensioned sothat a material basket 32 held thereby can be positioned over thecharging opening 42 of the projection 40. The changing device isdesigned so that the arms 34, and also the material baskets 32, can belifted upwardly in the direction of arrow A (see FIG. 2) or can belowered downwardly in the opposite direction.

[0045] In that respect, the charging apparatus 30 is designed so thatthe empty material basket 32 (at the left in FIG. 2) can be lifted by alifting movement in the direction of the arrow A. In addition, the emptymaterial basked 32 can be exchanged for the full material basket 32 (atthe right in FIG. 2) by rotating the changing device 180° about the axis35 and the full material basket 32 can then be lowered onto theprojection 40 over the charging opening 42 by a lowering movement in thedirection opposite of arrow A. Therefore, the material baskets 32 arealways held by the arms 34 of the changing device 30 and are not carriedby the projection 40. The transition between the material baskets 32 andthe projection 40 can be sealed off in a suitable manner, for example byusing skirts.

[0046] In the embodiment shown in FIGS. 1 to 4, the arms 34 are liftedupwardly as a whole in the direction of arrow A and are lowered in theopposite direction. In the alternative, as can be seen from FIG. 9, thechanging device can be provided with cantilever arms 34 that areindividually pivotable about a horizontal axis 36 or with cantileverarms 34, which are pivotable in the manner of a rocker member about ahorizontal axis 36. This design configuration, in which the arms 34 arepivotable about the horizontal axis, affords a further saving in termsof reducing the height requirements of the building of the steel works.This embodiment is therefore to be preferred when there are particularrequirements for a reduction in height.

[0047] An embodiment of the material basket 32, which is in the form ofa scrap basket, is shown in greater detail in FIG. 10 in the conditionin which the scrap basket 32 is supported on a carriage 80. As can beclearly seen from the plan view in FIG. 4, the scrap basket 32 has arectangular cross-section in the horizontal direction. Projections 32 aare provided at the side walls corresponding to the longer sides of therectangle, which projections 32 a enable engagement with the holdingelements 91 of a crane 90 (see FIGS. 2 and 9). A shaft 31 a is providedat the underside of those longer side walls and fingers 31 of theretaining means (retaining member) are mounted/pivoted thereon. Thefingers 31 have a length that substantially corresponds to half thelength (preferably somewhat more) of the short side of the rectangularshape, as can be clearly seen from FIG. 10. The fingers are laterallyspaced from each other in such a way, for example at a spacingcorresponding to their width, that an intervening space is provided forgas to pass therethrough. The fingers 31 are pivotable about the shafts31 a by means of an actuating member 35 in order to close and open theunderside of the scrap basket 32. The actuating member 35 has ahydraulic cylinder 35 a and a lever arrangement 35 b, which pivots thefingers 31 about the shaft 31 a in the described manner, as can be seenfrom FIG. 10. The actuating member 35 can be provided either only on oneshort side or on both short sides of the scrap basket 32.

[0048] The scrap basket 32 is loaded at a storage area for the chargingmaterial, for example at a storage area where the collected scrap isstored for the steel works. When the scrap basket 32 is loaded, thefingers 31 are supported from below at their free ends by a support 81that is provided on the carriage 80. Therefore, during the loadingoperation of the scrap basket 32, both ends of the fingers 31 are firmlysupported, thereby forming a stable lower boundary for the scrap basket32.

[0049] The internal space of the scrap basket 32 has a predeterminedvolume C and is lined with heat-retaining panels (thermopanels) 37,which are cast steel panels in the preferred embodiment. The fingers 31are cut from steel ingots in the preferred embodiment and have across-section of about 300 mm (horizontal)×200 mm. Depending on therespective requirements involved, the lengthwise dimension can beselected to be different, but the thickness should be not less than 100mm.

[0050] The scrap basket 32 does not have water cooling either at thefingers 31 or at the side walls 37.

[0051] In addition, at the scrap storage location, the scrap basket 32is loaded in portions of the total filling quantity, e.g., by aprocedure in which 3 to 5 tonnes of scrap is loaded in one operation byan excavator or the like into the scrap basket, which has a capacity forexample of 50 t or 80 t, thereby minimizing the dynamic forces involvedduring the loading operation. Therefore, the self-supporting structureof the scrap basket 32 is not required to bear the high dynamic forcesthat occur when charging 50 or 80 tonnes of scrap all at once into theshaft of a conventional furnace. The structure of the scrap basket 32 istherefore only designed to hold the weight, and not to receive thedynamic forces that are produced when 80 tonnes of scrap drops from aheight of 6 meters. This structure saves on costs and considerablyreduces the outer dimensions in comparison with a shaft having the sameinternal volume.

[0052] The scrap basket 32 shown in FIG. 10 has an approximatelyrectangular cross-section. In another embodiment of the scrap basket, atleast one side wall, which in operation in the position on theprojection 40, faces towards the electrode arrangement 70 (the sidewall, at the left in FIG. 4, of the scrap basket disposed above theprojection 40) has a convex configuration. The outside wall has a radiusof curvature in the horizontal direction that corresponds to the radiusR (see FIG. 4) of the pivotal movement of the outside wall about theaxis 35 during the rotational movement of the rotary tower 33. By virtueof this arrangement, the basket can have a greater volume and can bemounted closer to the electrodes without colliding with the electrodes71 or the electrode arrangement 70 during pivotal movement.

[0053] It is clear that one or more of the other outside walls can alsohave a convex configuration in order to increase the volume of theinternal space. In that case, it is possible to select the same radiusof curvature so that the scrap basket can be used in both possibleorientations. In the alternative, the side wall, which arranged inopposite relationship to the electrode arrangement, can be, for example,conformed to the outside shape of the vessel wall. It will beappreciated that, in this embodiment, the shape of the projection 40 isalso conformed in horizontal cross-section to the horizontalcross-section of the scrap basket 32 to the one or more convex outsidewalls.

[0054] Alternatively, it is also possible for the scrap basket 32 andthe projection 40 to be designed such that the scrap basket 32 has arectangular cross-section, as viewed in section in the horizontaldirection, such that the corners of the scrap basket in the positionabove the projection 40 project beyond the circle of radius R (see FIG.4). In this case, during the pivotal movement of the basket about theaxis 35, the corners of the scrap basket 32 would collide with theelectrodes. To avoid that situation, the arm 34 is designed so that,prior to the rotational movement, the scrap basket is moved radially inthe direction of the rotational axis 35 until the corners are on orwithin the radius R, which then precisely no longer collides with theelectrodes. Thus, collision avoidance can be effected, on the one hand,by movement in the horizontal direction or, as is possible for examplewith the embodiment shown in FIG. 9, by pivotal movement about ahorizontal axis 36 that also has a radial component.

[0055] The furnace of the first embodiment also has an extraction hood50 that is movable upwardly and downwardly in the vertical direction andthat is suspended substantially perpendicularly above the projection 40.The extraction hood 50 is connected via a waste gas conduit 63 to themain waste gas conduit 62. A controllable valve flap 65 is provided inthe waste gas conduit 63. The extraction hood 50 can be lowered togetherwith the waste gas conduit 63 in the direction of arrow B (see FIG. 3)or can be lifted in the opposite direction. That lifting and loweringmovement is necessary to permit adequate free space for lifting andlowering the scrap basket 32 above the projection 40 when changing thescrap basket 32 or when tilting the furnace vessel for the tappingoperation (see FIG. 3).

[0056] The extraction hood 50 has a lower intake opening. Thecross-section of the lower intake opening is matched to the shape of theupper portion of the material basket 32, so that the extraction hood 50seals off the upper portion of the basket when it is lowered onto thematerial basket 32.

[0057] As can be clearly seen from FIG. 3, the furnace vessel 10 can betilted by means of the cradle 2 for the tapping operation (see thebroken-line illustration of the projection 40 in FIG. 3). In this case,the waste gas conduit 61 is designed so that it is variable in length bya suitable displaceable portion that slides within a sleeve.

[0058] Nozzles are provided on the projection 40 for injecting coal dust(or another fuel) and oxygen. A waste gas analyzer (not shown) isprovided at the post-combustion chamber 60, which waste gas analyzermeasures in real time the composition of the waste gas that is exhaustedfrom the post-combustion chamber 60. The nozzles (feed device) for fueland oxygen, as well as the valves 64 and 65 and the waste gas analyzer,are connected to a control system that can be programmed to control andregulate the waste gas composition.

[0059] The configuration of the first embodiment, as shown in FIG. 1,enables the arc furnace to operate as a shaft furnace. In this case, thematerial basket 32, which is positioned above the projection 40,performs the function of the shaft, which is covered at its upperposition by the extraction hood 50. The changing device can change thematerial basket 32 in about 30 seconds. As a result, the material in afirst material basket can be preheated during the refining period of thepreceding smelting procedure. When the furnace is refilled after thetapping operation of the preceding smelting procedure, that preheatedcharge of material can be charged into the furnace (see FIG. 2). Then, asecond material basket 32 (at the right in FIG. 2), which is filled witha second charge, can be positioned over the projection 40 within 30seconds so that that charge is preheated during the smelting operationof the first charge. Once again, the material basket 32 serves as ashaft.

[0060] If maintenance or repair operations will be carried out for thecharging apparatus 30 or the material baskets 32 or the like, the arcfurnace of the first embodiment, in the second configuration shown inFIGS. 5 to 8, can be operated as a conventional furnace with a cover(not as a shaft furnace) in order to avoid a complete stoppage ofoperation.

[0061] For that purpose, the charging opening 42 of the projection 40 isclosed with a cover 43. For the charging operation, the cover 20 withthe projection 40 (and the cover 43), as well as the electrodes 71, canbe lifted in a conventional manner and pivoted away. In the alternative,charging can be effected through the projection 40 after the cover 43has been lifted off.

[0062] The empty space in the projection 40, which is closed off by thecover 43, serves in that situation as a conventional furnace waste gasdischarge conduit.

[0063] As the second configuration does not differ in other respectsfrom the first configuration, a further description is not providedherein.

[0064] A second embodiment of the arc furnace of the invention is shownin FIG. 9. As has already been described above, in this embodiment thechanging device 33 is provided with cantilever arms 34 that areindividually pivotable about a horizontal axis 36. The arms 34 also canbe jointly pivoted as an arm of a rocker member about the axis 36.

[0065] As can be clearly seen from FIG. 9, and this applies with respectto all embodiments of the invention, the structural height above theshaft can be markedly reduced because there is no need to provide spacefor an additional scrap basket or charging material container that isheld by the crane 90 above the shaft or material basket 32 during thecharging operation.

[0066]FIG. 9 shows a cover suction arrangement 100 that is connected viaa waste gas conduit 101 to a waste gas disposal system. The waste gasdisposal system can be, for example, the post-combustion chamber 60 oranother apparatus.

[0067] In all embodiments, such an arc furnace is designed for aspecific amount of material to be smelted. Thus, for example, there are100 ton furnaces or 160 ton furnaces. Such an amount of material to besmelted corresponds to a specific volume of the batch material, forexample scrap.

[0068] In the embodiments of the invention, the furnace vessel and theprojection preferably are dimensioned such that the amount of scrap thatcorresponds to half the charge to be smelted (that is to say 50 tonnesin the case of a 100 ton furnace) extends in a loose material column,which is introduced through the projection 40 in the non-moltencondition, at a maximum as far as the height H2 (maximum filling height)of the projection 40. Therefore, the approximate volume of the furnacevessel that is occupied by a loose material column which extends fromthe lower edge 44 of the projection 40, which is closest to theelectrode arrangement 70, at an angle of 45° to the bottom of the lowervessel portion 11 and fills the part of the vessel that is below theprojection 40, substantially corresponds to the volume C of a materialbasket 32 (FIG. 2).

[0069] The lower edge of the suction intake opening 41, which is at theheight H2, is preferably slightly higher than the lower edge 44, whichis disposed towards the electrodes, of the projection 40, as can beclearly seen from FIG. 2. In FIG. 2, the loose material column formingthe charge C is slightly higher than the lower edge 44, which isdisposed towards the electrodes, of the projection 40, and thisrepresents an amount which is still tolerable, as will be clearhereinafter with reference to the description of furnace operation.

[0070] Operation of the arc furnace of the embodiments of the inventionin the first configuration will now be described.

[0071] During the refining period of a preceding smelting procedure, afilled scrap basket 32 is held by the changing device 33 above thecharging opening 42 of the projection 40 with the fingers 31 in theclosed position. As a result, the material in the scrap basket 32 isheated by the hot gases that rise between the fingers 31 and through thescrap basket 32. The residence time of the scrap basket 32 is about 20minutes, depending on what is referred to in the art as the “tap-to-tap”time (the time period between two tapping operations). In addition, thecast panels 37 lining the internal space also absorb heat and heat iscommunicated to the scrap. The top side of the scrap basket 32 is closedby the cover hood 50, whereby the gases rising through the scrap basket32 are passed to the post-combustion chamber 60.

[0072] After the tapping operation of the preceding smelting procedurehas been performed, the charge in the material basket 32 is charged byopening the fingers 31 when the electrodes 71 have been withdrawn fromthe vessel, which results in the condition illustrated in FIG. 2.Because the electrodes 71 have been withdrawn from the vessel, theelectrodes cannot suffer from breakage due to scrap falling on them.

[0073] After the unloading operation, the column of scrap is not so highthat the fingers 31 are prevented from pivoting back into the closedposition.

[0074] Therefore, the emptied material basket 32 is immediately closedand replaced by the next filled scrap basket 32 by appropriate operationof the changing device 33. For that replacement operation, the hood 50and the scrap baskets 32 are lifted, the cantilever arms 34 of the scrapchanging device 33 are then rotated by 180° about the perpendicularrotational axis 35, and then the filled scrap basket 32 and theextraction hood 50 are lowered in the direction of the projection 40(see the arrows B in FIG. 3). In the meantime, the electrodes 71 havebeen lowered again into the furnace vessel and, after the second scrapbasket 32 is in position, power is supplied to the electrodes formelting the charge from the first scrap basket.

[0075] During the rotational movement of the material baskets 32 aboutthe axis 35 (pivotal movement), the electrode arrangement 70 is notmoved in the horizontal direction away from the projection 40 or thematerial baskets 32. As was already described above, if the materialbasket 32 has a rectangular cross-section in the horizontal direction,the material basket 32 is designed such that the corners just avoidtouching the electrodes 71 during the pivotal movement. In thealternative, the material basket is first moved away from the electrodearrangement 70 in the horizontal direction (by horizontal movement or bypivotal movement about the horizontal axis 36) until the corners nolonger collide with the electrode arrangement 70 during the pivotalmovement. In another alternative, at least the side wall of the materialbasket 32 that is disposed towards the electrodes 71 has a convex shapewith the radius of curvature R of the circular path, which convex shapeavoids collision with the electrode arrangement 70 with a smallclearance. In all three cases, this design prevents the electrodearrangement 70 from having to be moved away from the projection 40 inthe horizontal direction.

[0076] When the charge from the first basket is being smelted, thematerial in the second scrap basket 32, which is positioned above thecharging apparatus 42, is preheated in the same manner.

[0077] Further, when the material from the first basket has beensmelted, the charge from the second basket is charged into the furnacevessel by opening the fingers 31 after the electrodes 71 have again beenwithdrawn from the vessel (in order to avoid electrode breakage due toscrap falling thereon).

[0078] As there is a relatively large molten bath in the lower vesselportion 11, the scrap of the second charge floats more strongly in thedirection of the side of the vessel that is remote from the projection40 in a horizontal direction. As a result, the column of solid scrapdoes not reach the height that is shown in FIG. 2 but is markedly lower.

[0079] At this time, the empty scrap basket 32 and the hood 50 are onceagain lifted and the empty scrap basket 32 is replaced by a full scrapbasket 32, which in the meantime has been placed on the other cantileverarm 34 by the crane 90. In that way, while the second charge is beingsmelted, the next charge, which is already provided for the nextsmelting operation, is preheated.

[0080] After the electrodes 71 have been lowered again, the secondcharge is now smelted so that thereafter a molten bath is formed fromthe first and the second charges.

[0081] In the described embodiment, the furnace vessel and the scrapbaskets are designed so that two charges are sufficient to completelyfill the furnace. It will be appreciated that it is also possible forthe corresponding dimensions of the furnace vessel to be modified insuch a way that a third or another fraction of the total furnace fillingamount is charged in one operation.

[0082] When changing the material baskets 32, the charging opening 42 isopened upwardly. In that condition, about 40 to 50% of the waste gasesare suctioned away through the extraction opening 41. The remainder ofthe waste gases rises upwardly due to the temperature thereof and themajority is collected by the upper extraction hood 50. The remainingwaste gases pass to the cover extraction arrangement 100 (see FIG. 9).

[0083] In comparison with known shaft furnaces, the extraction opening41 and the upper extraction hood 50 substantially reduce the loading onthe cover extraction arrangement 100, as is described hereinafter.

[0084] After the refining period for the molten bath consisting of thesmelted first and second charges, a tapping operation is performed in aconventional manner.

[0085] Thereafter, the above-described procedure is repeated.

[0086] If it is not possible to change the scrap baskets, for examplebecause repair operations are being performed, then the arc furnace canbe operated, in accordance with the embodiments of the invention, in thesecond configuration that is shown in FIGS. 5 to 8. Operation in thisconfiguration does not differ from the operation of a conventional arcfurnace. The description thereof will therefore not be provided herein.

[0087] The design of the arc furnace in accordance with the embodimentsof the invention, and the resulting possibility of the correspondinglydescribed operation thereof, permit the following advantages.

[0088] By virtue of the relatively short residence time of the materialbaskets 32 above the projection 40 (about 20 minutes in a smeltingoperation) and the replacement thereof by another material basket thatis filled with charging material at another location, the thermalloading on the fingers 31 and the side walls 37 is so low that it ispossible to omit water cooling.

[0089] In the present embodiments, the interchangeable material baskets32 are used instead of the conventional shaft and therefore, during thecharging operation, there is no need, as is the conventional practice,for the entire amount of the scrap to be charged into the shaft fromabove in one operation. Instead, because charging is effected inrelatively small portions into the material basket at the scrap storagelocation, the drop height of the scrap that will be charged in thedirection of the fingers 31, as well as the amount that will be chargedinto the material basket at the same time, are drastically reduced. Itis therefore possible to forego a complicated and expensive mountingarrangement for the fingers 31, and that results in a smaller structureand a considerable cost saving. As it is possible to forego watercooling for the fingers 31 and the side walls, there are also noproblems due to leakages that can be caused by scrap falling thereon.

[0090] The material baskets 32 replace the scrap baskets that arerequired in any event in scrap-processing steel works. Thus, noadditional expenditure is involved in this respect.

[0091] In conventional shaft furnaces, it was necessary to provide a wayto move the shaft for repair purposes. That function is now performed bythe changing device so that no additional expenditure worth mentioningis involved here.

[0092] In conventional shaft furnaces, a column of scrap extends intothe shaft at the beginning of the smelting operation. Therefore, on theone hand, the waste gas passing over the column of scrap was cold and,on the other hand, there was no possible way to regulate the waste gastemperature and/or the waste gas composition utilizing the heat that isalways present in the furnace.

[0093] The empty space that is always present in the projection 40, andin which there are the extraction opening 41 and the nozzles for fueland/or oxygen, easily makes it possible to control and regulate thewaste gas composition at any time during the smelting procedure. If forexample the waste gas temperature and in particular also that portionwhich is removed through the hood 50 and/or the cover extractionarrangement 100 is too low, then above the column of scrap, above whichthere exists always an ignition temperature (flash point) of about 500°C. (this applies simply because of the scrap which is preheated to about500° C.), by injecting carbon and/or oxygen, it is possible to producehot waste gas that is fed to the post-combustion chamber 60 via theextraction opening 41 and the waste gas conduit 61. The post-combustionchamber 60 includes the waste gas analyzer so that the optimumcomposition of the waste gases that are to be subjected topost-combustion in the post-combustion chamber 60 can be adjusted bycontrolling the flow of the fuel and the oxygen and the position of thevalves 64 and 65. In the same way for example an excess of CO can beeliminated by injecting oxygen into the projection 40.

[0094] The saving in terms of structural height above the furnace, whichis afforded by virtue of the horizontal interchangeability of thematerial baskets 32, has already been discussed above.

[0095] In comparison with a conventional arc furnace, the overall powerof the waste gas cleaning system can be reduced by about 60%, becausethe majority of the waste gases that escape are removed by theextraction opening 41 and the extraction hood 50, even when no materialbasket 32 is present.

[0096] The absence of the support structure for the shaft means that thematerial basket 32 can be placed significantly closer to the electrodearrangement 70. As a result, the horseshoe shape that is required in thecase of conventional shaft furnaces can be greatly reduced to the roundshapes that are more advantageous in terms of energy and structure.

1-16. (Cancelled)
 17. A metallurgical furnace comprising: a vesselhaving a maximum filling height defined therein, a cover coupled to thevessel, a projection mounted to one of the cover and the vessel andhaving a charging opening defined therein, a charging apparatus arrangedand constructed to charge material to be smelted into the vessel, thecharging apparatus comprising at least first and second self-supportingmaterial baskets arranged and constructed to be alternatively positionedabove the projection, each basket defining an internal space and havinga pivotable retaining means arranged and constructed to close anunderside of the basket, wherein at least one space is defined in thepivotable retaining means to permit passage of hot gas emanating fromthe vessel into the internal space, wherein the pivotable retainingmeans is pivotable into the projection when material to be smelted ischarged into the vessel, but the pivotable retaining means do not pivotbelow the maximum filling height, and means for positioning the materialbasket above the projection and for exchanging the fist material basketwith the second material basket.
 18. A furnace according to claim 17,further comprising an extraction opening defined in the projection. 19.A furnace according to claim 18, wherein the extraction opening isdefined below the range of pivotal movement of the retaining means. 20.A furnace according to claim 19, wherein the extraction opening isdefined above the maximum filling height.
 21. A furnace according toclaim 17, wherein the first and second material baskets each comprise atleast one heat-retaining panel disposed on at least one inner side wallthereof.
 22. A furnace according to claim 17, wherein the pivotableretaining means comprises a plurality of pivotable fingers, each beingpivotable to a position below a bottom edge of the side wall of thematerial basket.
 23. A furnace according to claim 22, wherein thefingers are steel fingers, each having a diameter of at least 100millimeters.
 24. A furnace according to claim 23, further comprising anactuating member mounted on each material basket, the actuating memberbeing arranged and constructed to actuate the pivotable fingers in orderto open and close the underside of the material basket.
 25. A furnaceaccording to claim 24, further comprising a cover arranged andconstructed to close the charging opening.
 26. A furnace according toclaim 17, further comprising an extraction device disposed substantiallyperpendicularly with respect to the projection and above the chargingdevice, the extraction device being arranged and constructed to removehot gases that rise upwardly through the projection.
 27. A furnaceaccording to claim 17, further comprising means for injecting at leastone of fuel and oxygen into the projection.
 28. A furnace according toclaim 27, further comprising a post-combustion chamber in communicationwith the projection and being arranged and constructed to incineratepollutants exhausted from the vessel.
 29. A furnace according to claim28, further comprising: a waste gas analyzer disposed at thepost-combustion chamber, and a controller arranged and constructed tocontrol the injecting means based upon instructions from the waste gasanalyzer.
 30. A furnace according to claim 17, wherein the changingmeans is arranged and constructed to pivot the material baskets in atleast one of a horizontal plane and a vertical plane in order toexchange the first material basket with the second material basket. 31.A furnace according to claim 17, further comprising: an extractionopening defined in the projection below the range of pivotal movement ofthe retaining means, but above the maximum filling height, an actuatingmember mounted on each material basket, wherein the pivotable retainingmeans comprises a plurality of pivotable steel fingers that arepivotable to a position below a bottom edge of the side wall of thematerial basket, the actuating member being arranged and constructed toactuate the pivotable fingers in order to open and close the undersideof the material basket, a cover arranged and constructed to close thecharging opening, an extraction device disposed substantiallyperpendicularly with respect to the projection and above the chargingdevice, the extraction device being arranged and constructed to suctionhot gases that rise upwardly through the projection, means for injectingat least one of fuel and oxygen into the projection, a post-combustionchamber in communication with the projection and the extraction deviceand being arranged and constructed to incinerate pollutants exhaustedfrom the vessel, a waste gas analyzer disposed at the post-combustionchamber, and a controller arranged and constructed to control theinjecting means based upon instructions from the waste gas analyzer, andwherein each material basket comprises at least one heat-retaining paneldisposed on at least one inner side wall thereof and the changing meansis arranged and constructed to pivot the material baskets in at leastone of a horizontal plane and a vertical plane in order to exchange thefirst material basket with the second material basket.
 32. Aself-supporting material basket suitable for receiving scrap metalcomprising: a plurality of side walls defining an internal space havinga cross-section that is substantially rectangular or convexly polygonalin a horizontal direction, the side walls being arranged and constructedto removably couple to a furnace vessel, and a plurality of fingerspivotably coupled via a shaft to a lower portion of at least one sidewall, wherein intervening spaces are defined between the plurality offingers for permitting gas to pass therethrough and wherein the fingersare arranged and constructed to be disposed in a closed position of anunderside of the internal space in a plane substantially perpendicularto the side walls and being adapted to be supported by a support meansdisposed on a carriage, and an actuating member coupled to the pluralityof fingers and being arranged and constructed to pivot the fingers so asto open and close the underside of the internal space.
 33. A materialbasket according to claim 32, wherein the material basket is arrangedand constructed to be held by a change device and to be pivotable withrespect to the furnace vessel along a first radius of curvature, and atleast one of the side walls has a convex configuration with a secondradius of curvature in the horizontal direction, the first radius ofcurvature being substantially equal to the second radius of curvature.34. A material basket according to claim 33, wherein the side walls andfingers are arranged and constructed to hold at least 50 tons of scrapmaterial.
 35. A material basket according to claim 34, wherein the sidewalls and fingers are arranged and constructed to withstand atemperature of at least about 500° C. for at least about 20 minutes. 36.A material basket according to claim 32, wherein the side walls andfingers are arranged and constructed to (i) hold at least 50 tons ofscrap material and (ii) withstand a temperature of at least about 500°C. for at least about 20 minutes.